I'm playing on the hardest setting with ironman turned on, boy did I facepalm when I entered the bear cave and thought my barbarian could take it...
You definitely need a tank or two at the hardest levels, I've learned to be VERY cautious when playing on the hardest setting.
That said, I've thus far only have had to restart 3 times (was so arrogant thinking I could do it with my main being a barbarian or wizard...) and I've got a strat down where I run from any large groups and try to pull only one or two at a time if I see a pack of anything.
Wouldn't have it any other way, easy mode is for whimps :-p